Yesterday, they called in the big guns and asked me to take a look at a problem involving a Dell Latitude E6420 in an e-port replicator/docking station being unable to use an external monitor as a second display. Serving as a fresh set of eyes for the problem, I didn’t get a whole lot more information than a description of the problem and a few red herring symptoms.
With a quick preliminary look, I confirmed the problem on this Windows 7 64-bit laptop and ruled out the symptoms that were false or unrelated. With a quick search of The Google, I came across a few threads that reported the problem on the same model or other Dells. Those threads steered me in the direction of looking at nVidia’s Optimus technology setting in the BIOS.
The nVidia Optimus technology is certainly interesting stuff. It promises a balance between battery life and graphics performance, completely automatic. If you’re on battery, your laptop might only use the more efficient Intel HD graphics but if you’re plugged in, you can tap into the power of the nVidia card.
Checking in the BIOS of this Latitude E6420, I found the Optimus setting under Video and saw that it was enabled. I unchecked the box even though the laptop was running a compatible operating system.
Upon logging into Windows after disabling Optimus, Windows found 3 new devices that were not there before (part of my preliminary check was diving into Device Manager) and installed the hardware for them automatically.
With Optimus disabled, the system did not behave how it was desired but it was consistent. If you powered up the laptop with the lid closed, the video would be successfully sent through the DVI cable plugged into the docking station to the monitor and display the signal. If you powered up the laptop with the lid open, the video would only come to the laptop’s attached display and it couldn’t even see the secondary monitor as an option.
Re-enabling Optimus in the BIOS, I seemed to be better off once in Windows again. At least it would show a second monitor as an option even if it didn’t work. To take my troubleshooting to the next step, I changed from using the DVI connection off the docking station and instead used a VGA cable and connected it to the monitor. After restarting, the monitor was automatically working as an extended desktop to the laptop. It also worked when the VGA cable was plugged directly into the laptop instead of the docking station.
I would say that it was a problem with the DVI output or cable but it worked just fine when Optimus was disabled and the laptop was booted with the lid closed. I also don’t know if I can conclude that it was just using VGA that led to the working scenario. It could be related to the 3 devices that were installed when Optimus was temporarily disabled and then VGA worked as an option.
The docking station has one VGA port, the laptop has another one. The docking station also has two DVI ports and two DisplayPort ports(?). I did not have a monitor with a DisplayPort input or a DisplayPort cable, so I could not test if that would have also failed like the DVI connection did.
The user saw that it was working, and consistently when placing the laptop in the docking station while it was already running or when it was powered on from the port replicator. I would hate to think it simply came down to “use VGA instead of DVI” but unless the other actions I took through troubleshooting had something to do with it, that would be the case.